The present invention relates generally to motor circuits, and more particularly, to motor circuits that involve multiple electronically commutated motors.
Convection air cooling is widely used in many industries, including the automotive industry. In automobiles, for example, heat from the internal combustion engine is transferred via coolant fluid to a radiator element, such as the radiator R shown in FIG. 1. The radiator element then employs air cooling to dissipate the heat from the heated coolant fluid. In a typical installation, a cooling fan F is supported within a shroud S to direct air flow across the radiator R.
In any event, the quantity of heat transferred by air cooling is related to the size of the fan, as well as other factors, including fan speed and blade shape. However, fan size is often limited by the environment in which the fan is used. For example, the fan size in an automobile is limited by the amount of available space in the engine compartment of the automobile. Because fans rotate, any increase in fan size requires additional space in every radial direction. In other words, a rotary fan, and especially its supporting shroud S, occupies a diameter D. Greater air flow requirements translate to a larger fan, which means a larger diameter D which, again, increases the profile of the fan in every radial direction.
One way to increase the effective cooling without requiring additional space in every radial direction is to employ multiple fans. For example, employing two identical, adjacent fans, such as the arrangement depicted in FIG. 2, increases air flow while only requiring additional space in one direction. As a result, two smaller fans, such as fans F1 and F2, may fit more conveniently than one large fan in an application that has excess room in the horizontal direction H but little or no excess room in the vertical direction V. A common shroud S can be provided to house both fans, while maintaining a compact profile.
Automotive cooling system applications particularly benefit from a multiple fan arrangement, such as the arrangement shown in FIG. 2. In many automotive designs, the use of two adjacent fans is more easily accommodated than a single large fan, especially for smaller vehicles. In one prior art automotive fan system, two electrically commutated (xe2x80x9cECxe2x80x9d) motors, designated as EC1 and EC2 in FIG. 3, are employed to rotate the respective fans F1 and F2. Associated with each motor EC1 and EC2 in such a system is a driver circuit that includes one or more drive switches, a snubber, and other elements typically associated with EC motors.
One drawback to the above system involves the necessity of various wiring elements and harnesses to deliver the DC power to the driver circuits and motors, as well as control information to the driver circuits. In particular, EC motors typically require signals that turn the various driver circuit switches on and off at appropriate times during the rotation of the motor. Such control signals may be used to control the speed of the motors. In general, the source of the control signals is the engine control unit (ECU) of the automobile, and the source of DC power is the vehicle battery.
Accordingly, multiple wires must be run to each of the two EC motors to allow control thereof. As shown in FIG. 3, each motor and associated control system EC1 and EC2 requires its own set of power supply lines V+ and Vxe2x88x92 and its own control signal wire CTRL1 and CTRL2. Thus, a separate wiring harness is required for each EC motor. Of course, the duplicate wiring harnesses increase the component requirements for the cooling system, and increases the number of components that can wear out. Perhaps more problematic is the need to route the wiring harnesses through the engine compartment, and the increased avenues for introducing RF interference into the motor control system. Naturally, these problems increases for each motor added to the cooling system.
Accordingly, there is a need for a multiple motor system that avoids these shortcomings and that is particularly suited for use as part of an engine cooling system. Such need exists particularly in the automotive field for use of the dual motors for cooling fan purposes.
The present invention addresses the above need, as well as others, by providing a motor circuit and associated method that employs multiple EC (electronically commutated) motors that are controlled via a single controller located on the shroud on or near where the motors are mounted. The use of a single controller reduces the amount of wires that must be run from a control signal generator and/or DC power supply to the motors.
In one embodiment of the present invention, a motor circuit includes a first EC motor circuit, a second EC motor circuit, and a controller. Each of the first and second EC motor circuits includes a switch, a commutation and protection circuit, and a power stage that are operable to power The controller provides PWM signals to each switch of the first and second EC motor circuits. The first and second motor circuits thereafter generate a motor speed responsive to a duty cycle of the PWM signals provided by the controller.
Preferably, the first and second motor circuits include motors to drive first and second fans mounted within a fan shroud, and the controller is affixed to the shroud and/or the motor of the first motor circuit. A single wiring harness provides a speed command to the controller from an external source, as well as power cables for the motors.
In another embodiment, a motor circuit includes a first EC motor circuit, a second EC motor circuit, and a controller. Each of the first and second EC motor circuits includes a switch, a commutation and protection circuit, and a power stage. The controller provides PWM signals to each switch of the first and second EC motor circuits. The first and second motor circuits thereafter generate a motor speed responsive to a duty cycle of the PWM signals provided by the controller. The controller is operable to generate the PWM signals such that the start and stop times of the positive duty cycles of the PWM signals are staggered.
Thus, embodiments of the present invention reduce the wiring requirements within a shroud supported dual motor set by employing a single speed PWM signal generating controller. Other embodiments reduce electromagnetic interference by staggering the start and stop times of the PWM signals to two fans.
The above described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings, which are embedded therein.